<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      #box::after {
        content: "!!";
        color: red;
      }
    </style>
  </head>
  <body>
    <div id="box">hello box</div>
    <script>
      const box = document.getElementById("box");

      console.log(box.style.color);
      console.log(box.style.width);

      // ---

      const style = getComputedStyle(box);
      console.log(parseInt(style.width));
      console.log(parseFloat(style.width));
      console.log(style.color);

      //---

      const styleAfter = getComputedStyle(box, "after");
      console.log(styleAfter.color);
    </script>
  </body>
</html>
